1. Technical Field
The present invention relates to a mask, a method for manufacturing a mask, a method for manufacturing an electro-optical device, and electronic equipment.
2. Related Art
An organic electroluminescent (EL) panel, which is a kind of electro-optical device, is made up of light-emitting, fast-response display elements having a multilayered structure of thin films. The organic EL panel forms a lightweight display that provides high-speed motion picture response, and thus has recently drawn great attention as the display panel of a flat panel display (FPD) TV, for example. A typical method for manufacturing such an organic EL panel is described in Applied Physics Letters, Vol. 51, No. 12: 913-14, 1987. Specifically, a transparent anode made of indium tin oxide (ITO), for instance, is patterned by photolithography in a desired pattern. Then, an organic material is deposited on the pattern with a vacuum evaporator. On top of that, a cathode film of a low work function metal, such as MgAg, is evaporated to form a cathode.
Light-emitting elements arranged this way are finally sealed in an inert gas atmosphere so as not to come in contact with moisture or oxygen.
The organic EL panel can emit light of various colors by changing light-emitting materials. For example, a technique for forming red, green, and blue light-emitting elements for individual pixels with a thin, highly fine metal mask has been proposed. This technique is to make a metal mask and glass substrate stick together with a magnet and perform evaporation through the mask in order to manufacture a full-color organic EL panel that provides sharp images (see Japanese Unexamined Patent Publication No. 2001-273976, for example).
To perform evaporation with a mask, a technique for manufacturing an evaporation mask using a silicon substrate has been developed. This method employs semiconductor manufacturing techniques, such as photolithography and dry etching, and develops the silicon substrate into a mask.
Since the thermal expansion coefficient of silicon is almost equal to that of glass, no displacement occurs between the silicon mask and a glass substrate on which a film is deposited due to thermal expansion. In addition, using silicon can enhance processing accuracy (see Japanese Unexamined Patent Publication No. 2001-185350, for example).
The metal mask described in Japanese Unexamined Patent Publication No. 2001-273976 has the following problem. To increase the panel size for a larger organic EL panel, it is necessary to make the metal mask used for the panel correspondingly larger. It is, however, difficult to manufacture a large and thin metal mask with a high degree of accuracy. Furthermore, the thermal expansion coefficient of the metal mask is much larger than that of the glass substrate used for the organic EL panel. Therefore, the metal mask expands much more than the glass substrate because of thermal radiation during evaporation. As a result, variations due to the thermal expansion accumulate and become considerable when manufacturing a large organic EL panel with the metal mask. It is therefore considered that the metal mask can be used for manufacturing small- or middle-sized panels of about 20 inches at most.
The evaporation mask using the silicon substrate described in Japanese Unexamined Patent Publication No. 2001-185350 has an opening with a predetermined pattern formed by crystal anisotropic etching. The corners of the opening are almost right-angled or sharp-angled. The problem is that stress tends to be concentrated in the corners of the evaporation mask described in Japanese Unexamined Patent Publication No. 2001-185350, and the mask is easily broken once a force is applied to it. Therefore, it is impractical to use the evaporation mask using the silicon substrate described in Japanese Unexamined Patent Publication No. 2001-185350 in equipment manufacturing sites.
In consideration of the above-described problems, the present invention aims to provide a silicon mask with high mechanical strength that is hard to break; a method for manufacturing such a mask; a method for manufacturing an electro-optical device; and electronic equipment.
The present invention also aims to provide a mask that is applicable to a larger area in which a film is deposited and capable of patterning a thin film with a high degree of accuracy, and whose corners are resistant to breakage (are hard to break) and endure repetitive use; a method for manufacturing such a mask; a method for manufacturing an electro-optical device; and electronic equipment.